Plastic films have widely been employed for use in, such as supermarkets and the like, for prepackaging various products including foods, such as vegetables and the like. See, for example, U.S. Pat. No. 6,489,016 which discloses multilayer packaging films of polyolefin. Also disclosing such packaging materials and packages made therefrom are U.S. Pat. Nos. 6,383,582; 5,750,262; 5,783,270; and 5,755,081; and Statutory Invention Registration No. H1727. Such prepackaging films serve for covering and enclosing commercial articles, such as foodstuffs including liquid foodstuffs, as individual articles or in a lot allotted or subdivided into small portions placed on a plastic carrier tray or the like. The success of such flexible packaging has been attributed to the broad use of thermoplastic heat sealants that are capable of providing the highest degree of package integrity, security and durability.
Furthermore, it is required for the prepackaging film that the film should be transparent and can easily be cut with an adequate extensible elasticity and an ability for adhering onto various surfaces, together with practical performance attributes such as resistance to fogging on the inner face when packaged, resistance to break-through upon heat sealing due to the heated pressing by the sealing bars, restorability from finger pressing and superior heat-sealability.
As is also well known, a “heat-seal” refers to the union of two films, e.g., a film and a thermoformed film/container or two portions of the same film, by bringing the films into contact with one another and then applying sufficient heat and pressure to the contacting regions of the films to cause the films to fuse together. Conventionally, but not necessarily always, the heat-seal is continuous and encircles the product to completely enclose the product within the two films, and is formed by a mechanism that includes a heated element (often referred to as a “seal-head”) which is pressed onto the contacting regions of the films from one side of one of the films and typically presses the films against a non-heated backing element so that the films are pressed between the heated element and backing element for a period of time sufficient to effect a heat-seal. Alternatively, the films can be pressed between two heated elements or jaws to effect a heat seal.
The heat seal performance of thermoplastic materials is a complex function of time, temperature and pressure. J. R. de Garavilla, Tappi Journal, 191 (June 1995) describes the sealant performance of various ionomer, acid copolymer and metallocene polyethylene resins.
Packaging films from thermoplastic resins are typically made by melt extrusion. For melt extrusion, melt strength and extrusion processability of the polymer resin are some important characteristics. Resins capable of higher extruder output and requiring less energy to convert into film are preferred. Heat sealability at low temperatures (i.e., under 80° C.) is beneficial since it is more amenable to many commercial processes and allows for higher production speeds.
An object of the present invention is to provide a film for packaging applications. In particular it is an object of the present invention to provide films that can be heat sealed at relatively low temperatures and methods of packaging comprising films that can be heat-sealed at relatively low temperatures. It is a further object to provide a film which optionally can be laminated to thermoplastic polymers or metals at relatively low temperatures.